JP3089349B2 - Handsfree phone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hands-free telephone capable of making a call without holding a handset, and more particularly to a hands-free microphone.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG.
In addition to the handset 2, there is also a hands-free telephone provided with a speaker 6 and a microphone 8 on the main body 4. With this telephone, the user can make a call while the handset 2 is left on the main body 4. In addition, 9 is a push button.

In such a hands-free telephone, the speaker 6 is provided inside the back side of the main body 4 so as to face forward.
The microphone 8 is located inside the front wall 5 on the front side of the main body 4.
As shown in FIG. 4, the microphone 8 is attached so that the front side faces the front wall 5. Reference numeral 10 denotes a sound collecting hole formed in the front wall 5.

[0004]

As shown in FIG. 4, the distance a from the central axis of the microphone 8 to the upper surface 12 of the desk is:
When the length of the sound wave becomes １ ／, the sensitivity of the microphone 8 is significantly reduced. This is caused by the sound wave being reflected by the upper surface 12 of the desk, and the sound wave of the reflected sound having undergone a half-wavelength path difference in a round trip and the sound wave before reflection interfering in opposite phases. For example, if the distance a is 20 mm, the wavelength of the sound wave in which such out-of-phase interference occurs is 80 mm. If the speed of sound in the air is 340 m, the frequency f in which out-of-phase interference occurs is 4.25 KHz ( = 340m / 80
mm).

In general, the maximum transmission frequency of a telephone line is 3.5 KHz, so if the distance a is 20 mm,
No anti-phase interference occurs in the transmission frequency band (0 to 3.5 KHz). However, if the maximum transmission frequency is increased in order to improve the sound quality of the telephone, a frequency at which interference of opposite phase occurs in the transmission frequency band is likely to be present.
For example, if the distance a is set to 20 mm and the transmission frequency band is expanded to 7 KHz as described above, the interference of the opposite phase occurs at 4.25 KHz as described above, so that the 4.25 KHz sound wave is transmitted. The microphone 8 cannot pick up sound, and high sound quality cannot be achieved.

In order to solve this problem, the distance a may be reduced so that the frequency at which the interference of the opposite phase occurs is higher than the maximum transmission frequency. For example, if the distance a is 10 mm, the anti-phase interference occurs at a frequency of 8.5 KHz, which is higher than the maximum transmission frequency of 7 KHz.

However, there is a limit in reducing the distance a due to the relationship between the diameter d of the microphone, the thickness t of the bottom wall 7 of the main body 4, the height h of the legs 14 of the main body 4, and the like. For example, d =
Assuming that 15 mm, t = 3 mm, and h = 5 mm, the distance amin is 15.5 mm (= d
/ 2 + t + h), and the anti-phase interference is about 5.4.
Occurs at 84 KHz.

[0008] The present invention provides for interference in opposite phases to occur at frequencies higher than the highest transmission frequency in a telephone,
The purpose is to achieve high sound quality.

[0009]

In order to achieve the above object, the present invention relates to a hands-free telephone having a speaker and a microphone provided in a main body. And the microphone is provided on the floating bottom wall portion such that the front side thereof is in contact with the floating bottom wall portion. Further, the distance from the front of the microphone to the mounting surface described above may be selected so that the value obtained by dividing the sound speed by four times this value is greater than the maximum transmission frequency of the hands-free telephone. it can.

[0010]

According to the present invention, the front side of the microphone is attached to the floating bottom wall portion in contact with the floating bottom wall portion. Therefore, the distance from the front side of the microphone to the mounting surface can be shortened, and the frequency of the sound wave that causes the anti-phase interference can be increased.

[0011]

FIG. 1 shows a first embodiment. This example is
It has a main body 20. Although not shown, the main body 20 is formed in the same shape as the main body 4 shown in FIG. The speaker 6 shown in FIG.
A speaker is provided facing the front as in FIG.
A handset similar to the handset 2 shown in FIG.

The main body 20 has a uniformly flat bottom wall 22, and a plurality of legs 24 are provided on the outer surface side of the bottom wall 22 at predetermined intervals. The wall 22
The mounting surface of the main body 20, for example, from the upper surface 25 of the desk to the
Floating only at the height of

The bottom wall 22 on the near side (left side in FIG. 1) of the main body 20 is provided with a plurality of sound collection holes 26 penetrating therethrough. A microphone 28 is provided in the main body 20 in contact with these sound collection holes 26. The microphone 28 is, for example, a non-directional microphone formed in a cylindrical shape, and is provided with its front side, that is, a state in which the sound pickup portion is in contact with the sound pickup hole 26.

In other words, the microphone 28 is provided in the main body 20 with its front side facing the upper surface 25 of the desk.
The distance b up to 5 is t + h, where t is the thickness of the bottom wall 22 and h is the height of the legs 24.

That is, since the microphone 28 is provided as described above, the distance b is d / 2, which is even included in the shortest distance amin (= d / 2 + t + h) in the conventional device shown in FIG. Is not included, and the distance b is the distance a
It can be shorter than min.

For example, assuming that t = 3 mm and h = 5 mm as shown in connection with FIG. 4, the distance b is 8 mm, which is about 1/2 of the distance amin (= 15.5 mm). Therefore, in the case of the distance b, the frequency at which the interference of the opposite phase occurs is 10.625 KHz [= 340 m / (8 mm *
4)], and even if the maximum transmission frequency of the telephone of this embodiment is increased to 7 KHz shown in connection with the conventional example of FIG. 4, interference of opposite phases occurs in the transmission band (0 to 7 KHz). Does not occur, and the sound quality can be improved. In addition, by adjusting the height h of the leg 24, the frequency at which interference of opposite phases occurs can be adjusted to a desired frequency.

FIG. 2 shows a second embodiment. In this embodiment, the bottom wall 22a of the main body 20a is not uniformly flat,
The configuration is the same as that of the first embodiment, except that the central portion protrudes toward the upper surface 25 of the desk. The same parts are denoted by the same reference numerals, and description thereof will be omitted.

Also in the case of the second embodiment, since the front side of the microphone 28 faces the upper surface 25 of the desk, the distance b1 from the front side of the microphone 28 to the upper surface 25 of the desk is equal to the distance of the microphone 28. 4, the distance from the central axis of the microphone 28 to the upper surface 25 of the desk when the microphone 28 is attached to the front wall 30 so that the front side faces the front wall 30 of the main body 28a can be made shorter. Therefore,
The value obtained by dividing the sound speed by a value obtained by multiplying the distance b1 by 4 is the frequency at which the interference of the opposite phase occurs. For example, the leg 24 is set so that the frequency becomes higher than the maximum transmission frequency transmitted by the telephone of this embodiment. By adjusting the height of the telephone, the distance b1 can be set, and the sound quality of the telephone can be improved.

In both of the above embodiments, the legs 24 are provided on the bottom wall 22 or 22a, but the center of the bottom wall 22a is protruded toward the upper surface 25 of the desk as in the embodiment of FIG. , The leg 24 can be removed. In this case, since the upper surface 25 of the desk is located at the position shown by the dotted line in FIG. 2, the distance from the front side of the microphone 28 to the upper surface of the desk can be further reduced by the absence of the legs 24, and more and more. The frequency at which antiphase interference occurs can be increased.

[0020]

As described above, according to the present invention, the distance from the front side of the microphone to the mounting surface of the telephone can be shortened.
The transmission frequency can be higher than the highest transmission frequency of the telephone, and the sound quality of the telephone can be improved. Also, since the front side of the microphone faces the bottom wall side of the main body, the sound collecting hole is naturally provided on the bottom wall, so that dust and water can be prevented from entering the inside of the main body from the sound collecting hole. .

[Brief description of the drawings]

FIG. 1 is a partially omitted vertical sectional view of a first embodiment of a hands-free telephone according to the present invention.

FIG. 2 is a partially omitted longitudinal sectional view of the second embodiment.

FIG. 3 is a perspective view of a conventional hands-free telephone.

FIG. 4 is a partially omitted vertical sectional view of the hands-free telephone of FIG. 3;

[Explanation of symbols]

 20 20a Main body 22 22a Bottom wall 25 Top surface of desk (mounting surface) 28 Microphone

Claims (1)

(57) [Claims] 1. A hands-free telephone provided with a speaker and a microphone in a main body, wherein the main body is formed so that at least a part of a bottom wall is floated above a mounting surface of the main body, and the microphone is mounted on the main body. The sound speed is set to a value obtained by quadrupling the distance from the front side of the microphone to the mounting surface described above, provided on the floating bottom wall with the front side facing the floating bottom wall side. A hands-free telephone selected so that the value obtained by the division is greater than the highest transmission frequency of the hands-free telephone.